After graduation from Waseda University, Wakamoto initially found employment as a police officer assigned to the Tokyo Metropolitan Police Department's Anti-Riot Squad division before becoming a voice actor.

The quality of Wakamoto's voice is known for uniting astringency and sharpness, usually leading him to villain roles in dubbing work and games. Examples include Oskar von Reuenthal in Legend of the Galactic Heroes, Johnny in the Guilty Gear series, Barbatos Goetia in Tales of Destiny 2, Charles zi Britannia in Code Geass, Black Shadow in F-Zero GP Legend, Xemnas in the Kingdom Hearts series, Oda Nobunaga in Sengoku Basara, Cell in Dragon Ball Z, and Count Dracula in the Castlevania: Dracula X , and DIO from JoJo's Bizzare Adventures drama CDs. Nonetheless, Wakamoto has played numerous less antagonistic roles and has even lent his voice to comedic roles including Mechazawa in Cromartie High School and Onsokumaru in Ninja Nonsense.

He is best known for voicing Cell in Dragon Ball Z (including movies and games), M. Bison in the Street Fighter IV series and Nobunaga Oda in the Sengoku Basara series. He also voiced Xemnas in the Kingdom Hearts games.